netdev - Re: [PATCH] octeon_mgmt: Fix MIX registers configuration on MTU setup

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Message-Id: <20180718.131341.1949854699503730806.davem@davemloft.net>
Date:   Wed, 18 Jul 2018 13:13:41 +0900 (KST)
From:   David Miller <davem@...emloft.net>
To:     alexander.sverdlin@...ia.com
Cc:     netdev@...r.kernel.org, alexander.sverdlin@....com,
        steven.hill@...ium.com
Subject: Re: [PATCH] octeon_mgmt: Fix MIX registers configuration on MTU
 setup

From: Alexander Sverdlin <alexander.sverdlin@...ia.com>
Date: Fri, 13 Jul 2018 17:31:50 +0200

> From: Alexander Sverdlin <alexander.sverdlin@....com>
> 
> octeon_mgmt driver doesn't drop RX frames that are 1-4 bytes bigger than
> MTU set for the corresponding interface. The problem is in the
> AGL_GMX_RX0/1_FRM_MAX register setting, which should not account for VLAN
> tagging.
> 
> According to Octeon HW manual:
> "For tagged frames, MAX increases by four bytes for each VLAN found up to a
> maximum of two VLANs, or MAX + 8 bytes."
> 
> OCTEON_FRAME_HEADER_LEN "define" is fine for ring buffer management, but
> should not be used for AGL_GMX_RX0/1_FRM_MAX.
> 
> The problem could be easily reproduced using "ping" command. If affected
> system has default MTU 1500, other host (having MTU >= 1504) can
> successfully "ping" the affected system with payload size 1473-1476,
> resulting in IP packets of size 1501-1504 accepted by the mgmt driver.
> Fixed system still accepts IP packets of 1500 bytes even with VLAN tagging,
> because the limits are lifted in HW as expected, for every VLAN tag.
> 
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...ia.com>

Applied, thank you.